1. Field of the Invention
This invention relates to holographic recording and scanner systems and specifically to a holographic scanner which is both less expensive and at least as accurate as prior art holographic scanning systems.
2. Description of the Prior Art
U.S. Pat. No. 4,753,503 discloses a laser scanning system utilizing a laser beam conditioned to provide proper beam shape prior to the passage of the beam through a diffraction grating on a rotating holographic disc. Mirrors and similar optics allow the laser beam to be scanned along a straight line on a rotating drum for the recording of information. The system of the '503 patent uses a solid-state laser diode 11 together with collecting lens 12 to collect and collimate the output light from diode 11. The processed laser beam is then deflected by a holographic scanner consisting of a rotating disc with a plurality of diffraction gratings formed thereon to produce a rotating diffracted beam which is used to store information on a photoconductive surface. The system of the '503 patent uses optics to process the beam produced by the laser diode to ensure that the processed beam has the appropriate characteristics for use in generating a scan line on the photoconducting surface of the recording drum. The optics add cost to the scanning system.
Other laser scanning systems using holographic scanning discs and light beams for monochromatic light sources are disclosed, for example, in U.S. Pat. Nos. 3,721,486; 3,750,189; 3,951,509; and 4,094,576. In addition, papers such as the paper by Ih entitled "Holographic Laser Beam Scanners Utilizing an Auxiliary Reflector," published on page 2137 of the August, 1977 issue of Applied Optics (Vol. 16, No. 8) and by Pole et al. entitled "Holographic Light Deflection" on page 3294 of Applied Optics, Oct. 15, 1978, Vol. 17, No. 20 relate to holographic scanning systems utilizing monochromatic light sources.
Many of the holographic scanning systems of the prior art produce a scan line which varies in position as a function of variations in the frequency of the monochromatic light and in the angle of incidence of the scanning beam on the holographic disc due to wobble of the disc. In addition, in some cases the monochromatic light source is not truly monochromatic causing additional uncertainty in the location of the scan line.